completely regular
51Propaedeutic value of Esperanto — The propaedeutic value of Esperanto is the benefit that using Esperanto as an introduction to foreign language study has on the teaching of subsequent foreign languages. Several studies, such as that of Helmar Frank at the University of Paderborn …
52Cyrillic digraphs — Further information: List of Cyrillic digraphs Cyrillic script Slavic letters А Б В Г Ґ …
53Leap year — A leap year (or intercalary year) is a year containing one or more extra days (or, in the case of lunisolar calendars, an extra month) in order to keep the calendar year synchronised with the astronomical or seasonal year. For example, in the… …
54Metric space — In mathematics, a metric space is a set where a notion of distance (called a metric) between elements of the set is defined. The metric space which most closely corresponds to our intuitive understanding of space is the 3 dimensional Euclidean… …
55Topological group — Concepts in group theory category of groups subgroups, normal subgroups group homomorphisms, kernel, image, quotient direct product, direct sum semidirect product, wreath product …
56Closed set — This article is about the complement of an open set. For a set closed under an operation, see closure (mathematics). For other uses, see Closed (disambiguation). In geometry, topology, and related branches of mathematics, a closed set is a set… …
57Stone–Čech compactification — In the mathematical discipline of general topology, Stone–Čech compactification is a technique for constructing a universal map from a topological space X to a compact Hausdorff space beta; X . The Stone–Čech compactification beta; X of a… …
58Spirit leveling — is a technique for determining differences in height between points on the Earth s surface. It works by using a spirit level, an instrument consisting of a telescope and a tube level like that used by carpenters, rigidly connected. When the… …
59Andrey Nikolayevich Tychonoff — Infobox Scientist name = Andrey Tychonoff image width = 180px caption = birth date = birth date|1906|10|30|df=y birth place = Gzhatsk, Russian Empire death date = death date and age|1993|11|8|1906|10|30 death place = Moscow, Russia residence =… …
60Tikhonov — Tikhonov, sometimes spelled as Tychonoff ( ru. Тихонов), or Tikhonova (feminine; Тихонова) is a Russian last name and may refer to:;People *Aleksandr Tikhonov, a Russian biathlon athlete *Alexei Tikhonov, a Russian figure skater *Andrey… …
